1. Field of the Invention
The present invention generally relates to a lateral high voltage semiconductor device having an internal sense terminal and a method for sensing a drain voltage of the same. More particularly, the present invention relates to a thin layer, high voltage lateral silicon-on-insulator (SOI) device having a field plate terminal disconnected from a source terminal for the purpose of sensing a drain voltage.
2. Background Art
In the production of electronic consumer devices such as televisions, personal computers and the like, thin layer, high voltage, lateral silicon-on-insulator (SOI) semiconductor devices are often implemented. Such high voltage devices, however, are well known to be subject to a voltage overstress during transient conditions (e.g., switching). Since, the overstress voltage is often higher than the avalanche breakdown voltage, exceedingly high voltage and high current flow in the device often results. The capability of a device to sink this overstress energy is quantified as a xe2x80x9cruggedness specification.xe2x80x9d
For a lateral SOI device, the inherent ruggedness does not match that of vertical devices due to thermal limitations. Accordingly, a protection scheme is required. Various protection schemes can be used to improve the inherent ruggedness of semiconductor devices. For lateral SOI devices, protection schemes that avoid avalanche breakdown and associated current flow are important for a wide class of switch mode power supply (SMPS) applications.
Heretofore, attempts have been made to provide such a protection scheme. No existing scheme, however, provides an efficient way to sense drain voltage on an SOI lateral device based upon a voltage on a field plate. In contrast, conventional devices are provided with a field plate that is shorted to the source terminal/contact. As such, the field plate is not a separate terminal on which a voltage or current can be measured. Accordingly, such devices are not provided with an adequate internal protection scheme that affords the opportunity to make adjustments to avoid overstress voltage conditions.
In view of the foregoing, there exists a need for a scheme and method for sensing a drain voltage of a thin layer, high voltage, lateral SOI semiconductor device so that ample opportunity is provided to avoid overstress voltage conditions. Moreover, there exists a need for such a device that has a separate terminal for sensing drain voltage.
The present invention overcomes the drawbacks of existing schemes by provide a lateral semiconductor device having a sense terminal/electrode. Specifically, the present invention provides a lateral semiconductor device that has a field plate terminal disconnected from a source terminal for sensing a drain voltage of the device. Thus, the device of the present invention typically has at least five disconnected terminals: (1) a source terminal; (2) a gate terminal; (3) a drain terminal; (4) a substrate terminal; and (5) a field plate terminal. Under the present invention, the drain to field plate capacitance has a monotonic variation with voltage. This can be used to sense the drain voltage of the device through displacement current flow or voltage during a switching transient with a high degree of accuracy. In particular, by measuring the field plate voltage or current during a switching transient, the drain voltage can be accurately calculated. This provides the opportunity to make adjustments to avoid overstress voltage conditions.
According to a first aspect of the present invention, a lateral high voltage semiconductor device having a sense terminal is provided. The device comprises: (1) a buried oxide layer formed over a substrate; (2) a silicon layer formed over the buried oxide layer; (3) a top oxide layer formed over the silicon layer; and (4) a field plate terminal formed over the top oxide layer, wherein the field plate terminal is disconnected from a source terminal to sense a drain voltage of the device.
According to a second aspect of the present invention, a lateral high voltage semiconductor device having a sense terminal is provided. The device comprises: (1) a source terminal formed over a silicon layer; (2) a gate terminal formed over a top oxide layer; (3) a drain terminal formed over the silicon layer; (4) a substrate terminal formed on a substrate; and (5) a field plate terminal formed over the top oxide layer, wherein the field plate terminal is disconnected from the source terminal to sense a drain voltage of the device.
According to a third aspect of the present invention, a method for sensing a drain voltage of a lateral high voltage semiconductor device is provided. The method comprises: (1) forming a lateral high voltage silicon-on-insulator device having a field plate terminal disconnected from a source terminal; and (2) sensing the drain voltage by measuring a field plate voltage of the device.
Therefore, the present provides a device and method for sensing a drain voltage of a thin layer, high voltage, lateral SOI device.